The occurrence of semiconductor light-emitting diode (LED) leads to a reform of the lighting industry once again. Due to the advantages such as miniaturization and solidification, vibration resistance, fast instant startup, rapid response, energy-saving, long service life and environmental efficiency, the LED has been widely used in general lighting, backlight units and decorative lighting. The high-power and high-brightness LEDs have a great prospect in replacing incandescent lamps.
In industry, one way of producing white light is to coat a GaN-based blue LED with a phosphor powder. The GaN-based LED is of two basic structures, i.e., a lateral structure and a vertical structure.
For the LED with a lateral structure, two electrodes are located at the same side of the LED, and the current flows laterally in a GaN layer. As a result, a large resistance and a large quantity of heat will occur.
For the GaN-based LED with a vertical structure, two electrodes are located at both sides of the GaN-based LED respectively, and almost all the currents flow vertically through a GaN-based epitaxial layer. As a result, it is able to obtain uniform current distribution, a reduced resistance, an improved anti-static ability as well as reduced heat and voltage produced by the currents.
Due to the advantages of the GaN-based LED with a vertical structure, many big size companies in the LED industry have been studying the packaging process and manufacturing process for the vertical structure. Currently, there are a large number of packaging structures for the LED, and most of them need to use a gold wire, i.e., the gold wire is welded onto an electrode of the LED chip.
Because the electrode and gold wire welded on a light-extraction surface of the LED chip will prevent a portion of light from passing therethrough, the LED chip will have low light extraction efficiency and poor light extraction consistency. In addition, sophisticated instruments and complex processes are required for welding the gold wire, so the operation process is complicated and the cost is high.